Method of producing hydrocarbon gas

Abstract

A method of producing gas from an underground formation, which is penetrated by a production well to surface, the method including allowing formation fluid comprising gas and liquid to flow into the production well at a production interval; allowing the formation fluid to separate into a gaseous component and a liquid component; producing the gaseous component through the production well to the surface; accumulating the liquid component in the production well so as to form a liquid column having, at a drainage interval of the production well, a pressure exceeding the pressure in the surrounding formation; and allowing liquid from the liquid column at the drainage interval to drain away into the surrounding formation, comprising treating the wall of the production well at the drainage interval and/or treating the formation surrounding the drainage interval so as to increase the flow rate of liquid into the surrounding formation.

We claim:  
     
         1 . A method of producing gas from an underground formation penetrated by a production well, the production well extending to surface, the method comprising the steps of: 
 allowing formation fluid comprising gas and liquid to flow from the underground formation into the production well at a production interval;    allowing the formation fluid to separate into a gaseous component and into a liquid component;    producing the gaseous component through the production well to the surface;    accumulating the liquid component in the production well so as to form a liquid column having, at a drainage interval of the production well, a pressure exceeding the pressure in the surrounding formation; and    allowing liquid from the liquid column at the drainage interval to drain away into the surrounding formation,    wherein the step of allowing liquid from the liquid column to drain away comprises treating the wall of the production well at the drainage interval and/or treating the formation surrounding the drainage interval so as to increase the flow rate of liquid into the surrounding formation.    
     
     
         2 . Method according to  claim 1 , wherein the step of allowing liquid to drain away comprises arranging perforations in the wall of the production well at the drainage interval.  
     
     
         3 . The method according to  claim 1 , wherein the wall of the production well is treated by adding a chemically active agent to the liquid.  
     
     
         4 . The method according to  claim 3 , wherein the chemically active agent is an acid.  
     
     
         5 . The method according to claims  1 , wherein the surrounding formation is treated by generating fractures therein.  
     
     
         6 . The method according to claims  1 , wherein pressure pulses are applied to the liquid column.  
     
     
         7 . The method according to  claim 1 , wherein the step of allowing the formation fluid to separate comprises controlling the flow rate of the produced gaseous component in the production well to remain below a critical gas flow rate, such that formation fluid can separate in the production well in the absence of a dedicated separator.  
     
     
         8 . The method according to  claim 1 , wherein the step of allowing the formation fluid to separate comprises admitting the formation fluid to the inlet of a gas/liquid separator, the gas/liquid separator having outlets for the gaseous component and for the liquid component.  
     
     
         9 . The method according to  claim 8 , wherein the liquid received at the outlet for liquid of the separator is guided through a conduit to a position below the production interval.  
     
     
         10 . The method according to  claim 8 , wherein the gas/liquid separator is arranged in the production well.  
     
     
         11 . The method according to  claim 10 , wherein the formation fluid comprises liquid vapour or liquid dissolved in the gas, and wherein the gas/liquid separator in the production well is arranged above the depth, at which during normal operation liquid condenses from the formation fluid.  
     
     
         12 . The method according to  claim 8 , wherein the separator is arranged at the surface.  
     
     
         13 . The method according to  claim 1 , wherein, during normal operation, the gaseous component is produced continuously to the surface, and wherein liquid from the liquid column is allowed to drain away simultaneously with producing the gaseous component.  
     
     
         14 . The method according to  claim 1 , wherein, during normal operation, the production of the gaseous component is at intervals interrupted for a period long enough to allow sufficient liquid from the liquid column to drain away into the formation, so that the liquid column height is reduced to below a predetermined height.  
     
     
         15 . The method according to  claim 1 , wherein the gaseous component mainly consists of hydrocarbon gas, and wherein the liquid mainly consists of water.  
     
     
         16 . A production well for producing gas from an underground formation, which well extends downwardly from the earth's surface and is arranged to penetrate the underground formation, the production well comprising: 
 a production interval for allowing formation fluid comprising gas and liquid to flow from the underground formation into the production well; and    a drainage interval,    wherein the production well is arranged so that a liquid that separates during normal operation from the formation fluid is accumulated to form a liquid column covering at least partly the drainage interval, and wherein the drainage interval is arranged so as to allow liquid from the liquid column to drain away into the surrounding formation, by treating the wall of the production well at the drainage interval and/or treating the formation surrounding the drainage interval.    
     
     
         17 . A production well according to  claim 16 , further comprising a gas/liquid separator having an inlet for formation fluid, an outlets for a separated gaseous component and an outlet for a separated liquid component.